Elastin is an extracellular matrix protein that is ubiquitous in mammals. Elastin is found, for example, in skin, blood vessels, and tissues of the lung where it imparts strength, elasticity and flexibility. In addition, elastin, which is prevalent in the internal elastic lamina (IEL) and external elastic lamina (EEL) of the normal artery, may inhibit the migration of smooth muscle cells into the intima. Elastin in the form of solubilized peptides has been shown to inhibit the migration of smooth muscle cells in response to platelet-derived factors (Ooyama et al, Arteriosclerosis 7:593 (1987). Elastin repeat hexapeptides attract bovine aortic endothelial cells (Long et al, J. Cell. Physiol. 140:512 (1989) and elastin nonapeptides have been shown to attract fibroblasts (U.S. Pat. No. 4,976,734). The present invention takes advantage of these physical and biochemical properties of elastin.
Thirty to forty percent of atherosclerotic stenoses are opened with balloon angioplasty restenose as a result of ingrowth of medial cells. Smooth muscle ingrowth into the intima appears to be more prevalent in sections of the artery where the IEL of the artery is ripped, torn, or missing, as in severe dilatation injury from balloon angioplasty, vessel anastomoses, or other vessel trauma that results in tearing or removal of the elastic lamina. While repair of the arterial wall occurs following injury, the elastin structures IEL and EEL do not reorganize. Since these components play major structural and regulatory roles, their destruction is accompanied by muscle cell migration. There are also diseases that are associated with weakness in the vessel wall that result in aneurysms that can ultimately rupture, as well as other events that are, at least in part, related to abnormalities of elastin.
Prosthetic devices, such as vascular stents, have been used with some success to overcome the problems of restenosis or re-narrowing of the vessel wall resulting from ingrowth of muscle cells following injury. However, their use is often associated with thrombosis. In addition, prosthetic devices can exacerbate underlying atherosclerosis. Nonetheless, prostheses are often used.
Until relatively recently, the primary methods available for securing a prosthetic material to tissue (or tissue to tissue) involved the use of sutures or staples. Fibrin glue, a fibrin polymer polymerized with thrombin, has also been used (primarily in Europe) as a tissue sealant and hemostatic agent.
Laser energy has been shown to be effective in tissue welding arterial incisions, which is thought to occur through thermal melting of fibrin, collagen and other proteins. The use of photosensitizing dyes enhances the selective delivery of the laser energy to the target site and permits the use of lower power laser systems, both of which factors reduce the extent of undesirable thermal trauma.
The present invention combines the advantages of elastin-based products with the advantages of laser welding techniques, and provides a unique method of tissue repair and replacement. The invention makes possible tissue prostheses (particularly, vascular prostheses) that are essentially free of problems associated with prostheses known in the art.